Control system for an axial piston machine

ABSTRACT

An axial-piston machine having a pivotal output-controlling member is provided with an input member (remotely actuatable or controlled by hand) and a servo force amplifier between the input member and the control member. A cam is pivotally mounted in the housing of the machine and cooperates with a cam follower while a variable or replaceable lever mechanism is provided between one of these members and the cam arrangement to enable selective variation of the transmission ratio between the input member and the cam or between the cam and the output-control member.

11 1 3,911,792 [4 1 Oct. 14-, 1975 1 CONTROL'SYSTEM FOR AN AXIAL PISTON MACHINE [75] Inventors: Walter Heyl, Oberafferbach;

Karl-Heinz Bergmann, Feldkahl, both of Germany [73] Assignee: Linde Aktiengesellschaft,

\ I Wiesbaden, Germany 22 Filed: Oct. 19,1973 21 Appl. No.2 407,960

[30] Foreign Application Priority Data Oct. 20, 1972 Germany 2251628 [52] US. Cl. 91/505; 91/378; 91/387; 92/121 [51] Int. Cl. F013 3/00; F01B 13/04 [58] Field of Search 91/387, 378, 505; 92/121 [56]' References Cited v UNITED STATES PATENTS 1,241,624 10/1917 Guy 91/505 X 1,957,759 5/1934 Coates et a1. 91/378 X 2,403,913 7/1946 Ellis 91/387 X 2,411,705 11/1946 Benjamin.. 91/378 X 2,754,806 7/1956 Funston 91/378 X 2,879,754 3/1959 von Kienlin et a1. 91/378 X 2,952,244 9/1960 Krauss et a]. 91/378 X BUdZlCl'l dQ 91/505 X 3,139,037 6/1964 3,385,120 5/1968 Nott 74/89.]5 x 3,434,391 3/1969 Olmsted. 91/378 x 3,768,369 10 1973 Knutson 91/378 FOREIGN PATENTS OR APPLICATIONS 7 0,075 5 1965 Canada ..'91/505 1,325,616 3/1963 France... 91/378 712,022 7/1954 United Kingdom 91/378 Primary ExamtherMartin P. Schwadron Assistant ExaminerAbraha'm Hershkovitz Attorney, Agent, or Firm-Karl F. Ross; Herbert Dubno [57] ABSTRACT An axial-piston machine having a pivotal outputcontrolling member is provided with an input member (remotely actuatable or controlled by hand) and a servo force amplifier between the input-member and the control member. A cam is pivotally mounted in the housing of the machine and cooperates with a cam follower while a variable or replaceable lever mechanism is provided between one of these members and the cam arrangement to enable, selective variation. of the transmission ratio between the input member and the cam or between the cam and the output control member.

2011111115, 3 Drawing Figures US. Patent 0a. 14, 1975 Sheet 1 of2 3,911,792

US. Patent 0a. 14, 1975 Sheet 2 of2 3,911,792

CONTROL SYSTEM FOR AN AXIAL PISTON MACHINE CROSS-REFERENCE TO RELATED APPLICATION The present invention is related to the copending application Ser. No. 325,889 filed Jan. 22, 1973, now US. Pat. No. 3,834,281 by us jointly with another and entitled CONTROL SYSTEM FOR AXIAL PISTON MACHINES AND THE LIKE.

FIELD OF THE INVENTION The present invention relates to a control arrangement for an axial-piston machine having a predetermined transmission characteristic between an input element and the control element of a swingable-drum or pivotal-disk axial piston machine.

BACKGROUND OF THE INVENTION As observed in the above identified commonly assigned copending application and the prior publications set forth therein, an axial piston machine, e.g., a hydrostatic pump or hydrostatic motor, may comprise a rotatable cylinder drum having a plurality of angularly spaced cylinder bores, each of which receives a respective piston which is reciprocable parallel to the axis ofthe drum. The stroke or excursion of each piston determines the displacement of the machine and means is provided to control this displacement.

For example, a swingable-disk or pivotal-disk control system operates on the swash plate principle whereby the pistons engage directly or through a shoe a plate which may be inclined to the axis of the drum, the angle of inclination determining the excursion, stroke or displacement. When the plate or disk lies in a plane perpendicular to the axis of the drum, the machine is said to be in a neutral condition since the pistons have no excursion as they rotate about the axis or as the disk is rotated about the axis.

In a swinging-drum axial-piston machine, the plate against which the pistons bear is stationary with respect to inclination to a shaft axis although the drum is mounted for pivotal movement about an axis perpendicular to the axis of the drum. Here again the angle of inclination of the swingable dru'm determines the stroke or displacement ofthe machine.

Thus in both types of machines, there is a swingable element whose angular orientation about an axis perpendicular to the shaftaxis of the drum axis determines the fluid displacement of the machine. When this element is connected to a control system for varying the displacement of the machine, e.g. in accordance with servomechanism principles, it is effectively the output or controlled element of the regulating system.

It'has already been notedthat axial piston machines may be either hydrostatic pumps or hydrostatic motors and, indeed, the axial piston machine may function generally as a pump or motor depending upon the fluid flow direction. A typical application of a hydrostatic machine of the type with which the present invention is concerned is in a transmission of an automotive vehicle. Thus an electric motor or internal combustion engine on the vehicle may drive one or more hydrostatic axial piston pumps. The latter may be operated by a prime mover such as an internal engine. The, or each, pump is connected to one or more hydrostatic axial piston motors whose output shafts drive the wheels of the vehicle. The vehicle is operated by the manual or remote displacement of an input element of the control system to swing the pivotal or output element from a position in which it lies in a plane perpendicular to the drum axis (neutral position) to one in which the pivotal element is canted, titled or angularly displaced from its neutral position to effect pumping in one direction or the other, thereby forcing fluid through the axial piston motors in one .or'the other sense and driving the vehicle wheels in the forward or reverse direction.

It has already been pointed out that a servo-type control mechanism between input element and the output element is preferred and the present invention deals with improvements in the control systems between the input and the output element of a hydrostatic or axialpiston device in which the input element may be a manually or remotely actuatable member and the output element is a swingable part of the axial piston machine. A linearly displaceable pilot piston or valve member (input) is followed by the large or power piston (output) which is coupled with the displacementcontrolling member of the hydraulic machine.

Between the input element and the output element of the hydraulic machine a predetermined relationship of force transmission or motion transmission may be required and this relationship will be described below as a transfer function using systems-analysis terminology and dealing with the control mechanism between the input element and the output element as a unit for achieving the desired transfer function. The input, constituting a displacement of the input element, may be referred to as an input signal while the output (in the form of an angular displacement of the pivotal member of the axial piston pump) will be considered an output signal.

It will be appreciated that the transfer function or relationship between the displacement of the input element and the displacement of the output element will depend upon the particular requirements of the machine in question. In very general terms, however, one can consider a system in which the input element is to be angularly displaceable while the pilot piston of the servomechanism is linearly displaceable in accordance with the principles set forth previously. The transfer function of the control system thus must be such as will transform the angular input signal into a linear output signal which eventually is applied as an angular displacement ofth'e disk or the drum of the hydraulic machine.

OBJECT OF THE INVENTION It is the principle object of the present invention to provide an improved axial-piston machine of compact and economical construction with greater facility of control and adaptability to particular requirements than prior-art axial piston machines.

It is another object of this invention to provide an axial piston machine of more versatility than has hitherto been obtainable.

Still another object of this invention is to provide an improved control system for an axial piston machine.

SUMMARY OF THE INVENTION According to one aspect of the present invention a cam is provided between the input element and the output element of a control system for an axial piston machine and a cam follower is likewise employed to transform the angular displacement of the input element to a linear displacement of the input member of a servomechanism with a transfer function or characteristic that differs from the simple harmonic relationship obtained when a linearly moveable servo-device is pivotablly connected directly to the swingable member of an axial piston machine and a lever directly operates the servo input.

The invention thus relates to a control device for the pivotal displacement-controlling member of a variabledisplacement pivotal-drum or preferably, a pivotal-disk axial piston machine with the control system being built into the housing or mounted upon a housing portion affixed to or built onto the basic housing of the axial piston machine. The angularly displaceable cam member, according to the invention, may be a cam disk or disk segment. The terms cam and cam disk are intended here to mean a member which is in forcetransmitting relation with a follower member whether the follower member is urged against an external or internal surface contour or is received in a groove of the cam (slave cam); the cam disk is coupled with a selectively displaceable pivotal lever (controlled by hand or remotely actuated by a servomechanism or some other control or regulating device).

The purpose of interposing an arcuate cam contour between the angularly displaceable element and the pivotal axial-piston machine element (output-control element) is to vary selectively the transmission ratio or transfer function with which the pivotal output-control element is operated in response to the input differently at various portions of the operating range of the input element or the output element.

It is frequently desired to have a significant displacement of the input element correspond to a small angular displacement of the pivotal element (e.g., in the region of the neutral position of the latter) and, conversely, to have a relatively large angular displacement of the pivotal element (output element) correspond to a small stroke or displacement of the linear movable input element elsewhere in the range of displacement of the pivotal output element of the axial-piston machine.

This is is advantageous, for example, in the control of the axial piston pump of a hydrostatic transmission of a vehicle when, during starting, stopping or slow creeping movement of the vehicle, a greater sensitivity to displacement of the control or input element is desirable than is necessary at higher speeds.

Even with other types of axial piston machines, it is often desirable to provide finer control at low speeds than at high speeds. However, it should be understood that, depending on the cam contour, other characteristics can be obtained whereby at any portion of the operating range of the output element, a corresponding displacement of the input element is matched therewith. The same principle applies to the feedback of force to the input element whereby the latter may respond to the position of the output element of the axial piston machine.

Such a system is not always satisfactory as simply described above, especially where it is desired to vary the transmission characteristics from one axial piston machine to another. In this case, the cam must be replaced or a different cam provided in the housing. This is obviously inconvenient and involves considerable mechanical effort.

it is thus another object of the invention to provide a further advance over the systems of the latter type by increasing the versatility of a cam-type controlmovement regulator in an axial piston machine, by reducing the space necessary for the cam system in the housing, and by permitting a wide range of control with a cam of relatively small size.

The invention, in attaining the latter object, provides in a control chain as described a further transmission having input and output members and establishing a transmission ratio in terms of input forcezoutput force or input displacement: output displacement. Preferably this further transmission is a single or compound lever linkage and is adjustable so that the motion transfer between cam disk and input element or between the cam disk and the servomechanism can be varied and the same or substantially the same structural elements can be used to obtain a desired response of the outputcontrol element of the axial piston machine to an input signal.

The variability or adjustability of the additional lever linkage can be achieved by making at least one lever replaceable, i.e., removably interchangeable with another lever of a set. Alternatively, the point of attachment of one of the members of the cam system (cam member and follower member) can be varied along the length of the lever. For example, the cam follower may be longitudinally shiftable along a lever of the further transmission mechanism and can be locked in place at a selected location therealong. In this case it is possible to adjust the transfer function of the system simply by varying the effective lengths of the lever arms without major structural modification of the axial piston machine and especially without varying the axial spacing of the pivot axes.

With the system of the present invention it is possible to provide, with a fixed displacement of the input element (i.e., the lever which swings the cam) the relatively large adjustment stroke of a swingable drum machine or the relatively small stroke of an inclined-plate machine and vice versa. The cam disk makes it possible to provide different response characteristics for displacement of the control element in either direction from its neutral position or to provide different characteristics of the response of the hydraulic machine to displacement to different sides of the neutral position.

The control system of the present invention can be provided with a sensing pin or roller which engages the cam disk and is provided on a first lever which is connected with a shaft parallel to the shaft of the cam disk. With this shaft a second lever is connected and is longer than the first lever for engagement with the input element of the servoamplifier.

According to another aspect of the invention, a cam arrangement for controlling a hydraulic machine provided with a tilting displacement-control member and having an input element to which the output-control member is to respond, is provided wholly within the housing of the hydraulic machine and includes a cam disk. More particularly, the hydraulic machine is of the tiltable plate type and cam-follower means is provided between this tiltable plate and the cam disk while the servoamplifier is provided between the input element and the cam disk, the servoamplifier being likewise mounted on or incorporated in the housing of the hydraulic machine.

An advantage of the inclined disk machine over the swingable drum machine resides in the smaller size of the tiltable-plate machine and the fact that in most housings for machines of the latter type, the cam disk can be accommodated directly in the housing structure without requiring additional space externally thereof. The cam member, which can be relatively sensitive to mechanical action and corrosion, can thus be fully protected. the cam arrangement can be relatively small, there being preferably provided with a lever-type multiplication of displacement between the cam and the member actuated thereby. The lever transmission between the control member and the cam may be provided between the cam disk and the input element of a servoamplifier mounted on or disposed in the housing. The housing may be cast and formed integrally with an antechamber or space accommodating the servoamplifier and/or lever transmission and/or cam arrangement.

The lever transmission permits, for an inclined-disk machine, the use of the same servoamplifier arrangement as for a swinging-drum'machinein spite of the fact that the stroke of the input element of the servomechanism of the latter is greater than that which is required for the inclined-disk machine. Furthermore, it is possible with a lever transmission of this type to select the portion of an angular stroke over which the input element of the servomechanism is effective to be associated with the cam and other elements in the motiontransmitting train, to enable any desired response to be obtained.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a fragmentary axial cross-sectional view through an inclined-disk axial-piston pump embodying the invention;

FIG. 2 is a plan view of a portion of the system of FIG. 1; and

FIG. 3 is a diagrammatic cross-sectional view of a servomechanism suitable for use in the system of the present invention.

SPECIFIC DESCRIPTION The following description refers to a hydrostatic machine of the inclined-disk type and the drawing therefore shows only the control portion of a machine of this type. In general (as described in the aforementioned copending application), such a machine comprises a housing, a fluid-distribution plate or surface mounted in this housing and lying in a plane perpendicular to the axis thereof, the plate having intake and distribution ports connectable to a load such as a hydrostatic motor and communicating with cylinder bores of a drum rotatable about this axis and pressed against the fluiddistribution surface. The cylinder drum is connected to a shaft which passes through an opening of an inclinable disk with which the control mechanism of the present invention is associated. When this disk lies in a plane perpendicular to the axis of the drum, the angularly spaced axially shiftable pistons of the drum have no excursion and the machine is in a neutral position. When the disk is tilted about an axis perpendicular to the axis of the drum and the shaft, certain of the pistons as they sweep along one side of the disk are displaced inwardly into the respective cylinder bores while other pistons as they sweep along the opposite side of the disk are permitted to extend further from the respective cylinder bores to displace fluid from and induce fluid into the cylinder bores in a pumping action. The fluid is forced out of one of the ports of the machine and drawn into the other. The rate at which fluid is displaced, for a constant angular velocity of the drum, is a function of the degree of tilt of the disk since this determines the total displacement. When the disk is tilted in the opposite direction, the discharge port is transformed into an intake port and the erstwhile intake port becomes the discharge port. Similar principles apply to the inclined-drum machine in which the entire drum structure is tilted about an axis perpendicular to the drum axis to vary the stroke or displacement of the axial pistons. In this case the control arrangement is coupled to the tiltable drum.

In FIG. 1, the housing 1 of the tiltable-disk axial piston pump is provided with a pair of roller bearings 2 in which diametrically opposite stub shafts of the tiltable disk 3 are journaled. The control surface of the disk 3 is represented at 4 and the positions of the axially displaceable pistons have been represented in dot-dash lines in FIG. 1. The shaft is shown in section.

The disk 4 is provided with a pin 5 which extends transversely to the tilting axis in the plane of the paper of FIG. 1 to engage a pivotal member of a servoamplifier 6 in whose input element 7 a pin 8 engages. Pin 8 is received in a shaft 9 which is fixed to a lever 10 carrying the cam-follower roller 11. The roller 11 is received in a slave-camgroove 12 of a cam disk 13 mounted on a shaft 14 carrying a control lever 15.

Upon angular displacement of the lever 15, the shaft 14 is displaced to rotate the cam 13 about the axis of shaft 14. Since the groove or slot 12 is not circular and concentric with the axis of shaft 14, the cam-follower roller 11 displaces the lever 10 around the axis of shaft 9 which is rotated. The rotation of shaft 9 causes an angular displacement of the pin 8 in the plane of the paper of FIG. 2 about the axis of shaft 9 and thus displaces the input element 7 of the servoamplifier 6 perpendicular to the plane of the paper in FIG. 1. Since the lever 8 is longer than the lever 10, the displacement of the input element 7 of the servoamplifier 6 will be greater than the displacement of the follower roller 11 by the cam 12. Thus the displacement of the output element 5 of the servomechanism can be represented by the following relationship X= AT(x) where x is the displacement of the cam, T(x) is the transfer function representing the relationship of the input displacement x to the displacement of the cam-follower rollers and A is the multiplier represented by the lever linkage 10, 8. In this case, A is a constant.

The effective length of one of the levers may be adjusted by varying the position of roller 11 on lever 10 or the distance between the input element 7 of the servoamplifier and the axis of shaft 9. The transfer function of the cam may be varied by displacement of the cam. I

In addition, the lever 8 is slidably mounted in the member 7 which is pivotally connected to the valve of the servoamplifier such that the input element of the servoamplifier is displaced linearly when the lever 8 is swung about the axis of shaft 9.

In the neutral position of the pump, the lever 8 lies approximately perpendicular to the direction of displacement of the input member of the servoamplifier 6. In this construction, the cam disk 13 can be so designed that the radial distance between the cam groove or curve 12 and the axis of shaft 14 is smaller than the displacement of the input member 7 of the servoamplifier 6. The cam is provided directly in the housing of the machine together with the servomechanism and the lever arrangement and, for this purpose an antechamber may be formed directly adjacent the pump chamber and can be closable by a cover plate which allows access to the antechamber upon its removal.

In FIG. 3, we show a servoamplifier which may be employed with the system of FIGS. 1 and 2. In this servoamplifier, a cylinder 6a is formed in the housing 1 and is fed with hydraulic fluid by a pump 6b through a line 6c. The cylinder 6a is divided into two compartments 6d and 6e by a main piston 7a having a bore 7b receiving a pilot system 7c. The pilot system 7c is provided at its end 7d with a cylindrical body 7e rotatable about an axis perpendicular to the plane of the paper and slidably receiving the end 8a of the lever 8. Thus, as the lever 8 swings in the direction of arrow 8b, the cylindrical body 7e will be rotated in the clockwise sense and the end 8a of the lever will be slightly withdrawn from the cylindrical body as the pilot valve is displaced in the direction of arrow 7f. Hydraulic fluid under pressure is thereby permitted to flow via the passage 7g into the chamber 6d while the chamber 6e is connected to a fluid outlet, thereby causing the piston 7a to move in the direction of arrow 7funtil the piston 7a has been repositioned to correspond to the position of the lever 8 and the pilot valve. Conversely, when the pilot piston 7c is shifted in the opposite direction, the chamber 7d is connected to the drain side of the line while chamber 7e is pressurized and the piston 7a is driven in the opposite direction. The piston 7a, therefore, always follows the pilot piston and displaces the cylindrical body 5a about its axis 5b to similarly displace the pin 5 which is slidably received in this cylindrical body 5a.

We claim:

1. An axial piston machine comprising:

a housing;

an axial-piston arrangement in said housing and having an output;

a pivotal member in said housing engaging said axial piston arrangement for controlling said output;

an input lever externally of said housing and swingable to control the position of said pivotal member;

a first shaft extending through a wall of said housing and engaging said input lever while being rotatable thereby about a first fixed axis;

a cam affixed to said first shaft within said housing for rotation about said first fixed axis with said first shaft, said cam having a noncircular surface;

a cam follower in said housing engaging said surface;

a transmission lever within said housing including a first arm carrying said cam follower, a second shaft rotatable in said housing about a second fixed axis, and a second arm carried by said second shaft;

a linearly shiftable pilot piston in said housing engaged by said second arm for displacement in accordance with a predetermined response characteristic upon displacement of said input lever;

a follower piston fluid coupled with said pilot piston and responding to the displacement thereof for a following displacement; and

means connecting said follower piston to said pivotal member.

2. The axial piston hydraulic machine defined in claim 1 wherein said transmission lever includes adjustable means for varying the relationship between the displacement of said first arm by said cam and cam follower and the displacement of said pilot piston by said second arm. 

1. An axial piston machine comprising: a housing; an axial-piston arrangement in said housing and having an output; a pivotal member in said housing engaging said axial piston arrangement for controlling said output; an input lever externally of said housing and swingable to control the position of said pivotal member; a first shaft extending through a wall of said housing and engaging said input lever while being rotatable thereby about a first fixed axis; a cam affixed to said first shaft within said housing for rotation about said first fixed axis with said first shaft, said cam having a noncircular surface; a cam follower in said housing engaging said surface; a transmission lever within said housing including a first arm carrying said cam follower, a second shaft rotatable in said housing about a second fixed axis, and a second arm carried by said second shaft; a linearly shiftable pilot piston in said housing engaged by said second arm for displacement in accordance with a predetermined response characteristic upon displacement of said input lever; a follower piston fluid coupled with said pilot piston and responding to the displacement thereof for a following displacement; and means connecting said follower piston to said pivotal member.
 2. The axial piston hydraulic machine defined in claim 1 wherein said transmission lever includes adjustable means for varying the relationship between the displacement of said first arm by said cam and cam follower and the displacement of said pilot piston by said second arm. 